This application relates generally to the field of bolt catch assemblies, also referred to as bolt stop assemblies or bolt hold assemblies, incorporated into or combined with the lower receiver of semi-automatic firearms having multi-cartridge magazines to feed ammunition into the firearm. The bolt catch assembly holds the bolt in the open or recessed position when the magazine is empty, such that it is not necessary to re-rack the bolt when the empty magazine is exchanged for a full magazine.
To fire multiple rounds from a magazine-loaded firearm, the shooter firsts rack the bolt to load the first round from the magazine into the weapon. As successive rounds are fired, the magazine empties and a follower activates a bolt catch lifter, also called an activator arm or lift arm, to secure the bolt catch and prevent the bolt from advancing. When the empty magazine is replaced with a full magazine, firing may resume without the need to re-rack the bolt.
Bolt catch assemblies are well known. In a typical embodiment, the lift arm comprises an elongated linear segment pivotally mounted on its forward end to the lower receiver of the firearm. A follower flange or tab extends laterally over the magazine well of the lower receiver at a location where it is contacted by the magazine follower of an empty magazine, thereby elevating the free rearward end of the lift arm. The lift arm further comprises an L-shaped portion extending transversely across the body of the lower receiver, the L-shaped portion ending in an apertured structure that cooperates with an extension on the bolt catch, such that when the free end of the lift arm is pivoted upward, the bolt catch is raised and blocks the bolt from advancing. Upon replacement of the magazine, the bolt catch is manually released.
This known design for the lift arm utilizing a single pivot point results in a torqueing effect during operation, since the apertured structure on the end of the L-shaped portion that contacts the bolt catch is offset from the linear segment of the lift arm. This latch-style structure is flimsy and operates in a relatively loose manner since it is necessary to allow for some degree of play in the mechanism.
It is an object of this invention to provide a bolt catch assembly wherein the lift arm is structured as a C-shaped member, with each of the transverse legs of the lift arm being pivotally mounted to the lower receiver. It is a further object to provide a bolt catch assembly having an insert assembly for the cartridge ejector and magazine stop that does not require the use of lateral pins, the insert assembly being bolted from the top.